Nothing is worse than joining a Discord server and finding out it's enormous. You go to any given channel and the discussions are flying by so fast only people who are regulars can catch all the content but even then it's basically just noise.
Thread support was added to alleviate some of the noise problem but in communities that actually use them there's so many threads it's easy to lose track and everywhere else they're basically just strange ways of isolating yourself from the rest of the people in the community.
I'm not even sure what the point of a giant Discord server is. Like, I use Discord for organizing (online) activities, asking a question and getting it answered by a real expert, hanging out with friends, etc.
None of this scales, it's totally unworkable if you have 100+ people actively chatting, let alone thousands.
They can be useful as funnels into smaller, more intimate servers. During the pandemic, a couple of friends and I would play a fair amount of Among Us, which basically requires a full game of 10 people with at least moderate communication skills to be fun. You'd hop into one of these mega servers, join a voice call to fill in your missing players, and often times, if you weren't a foaming-at-the-mouth lunatic, you'd end up being invited to a smaller server to play future games. Once such a server gained critical mass that they no longer needed to resort to randoms for extra players, these private servers would start only growing via mutual acquaintance.
I never would have found the smaller servers, where at this point no one's playing the game we initially met through but are all friends, if not for bigger servers meeting the need of that entrance to the pipeline.
Conversely, I had a YT snowboarding person I followed start a Discord server with a few channels for chat, meetups and equipment swaps. Really cool, lots of good discussion and the community was really welcoming.
I stepped away and came back like a month later.
It had grown so fast, with so many users, there were suddenly like 50-60 channels, it was unreal how hard it was to keep track of anything happening. Even the original three channels were completely overrun with so many discussions and chats, I couldn't keep track.
So I had the experience of joining a small server, only to have it blow up when I came back and I just had to give up and moved on.
Thread support was added to alleviate some of the noise problem but in communities that actually use them there's so many threads it's easy to lose track and everywhere else they're basically just strange ways of isolating yourself from the rest of the people in the community.